1. Field of the Invention
This invention relates generally to thin film magnetic heads for high density data storage devices and, more specifically, to a self-aligned staggered-pole inductive head with a submicron track width.
2. Discussion of the Related Art
Thin film magnetic read/write heads are used for reading and writing magnetically coded data stored on a magnetic storage medium such as a magnetic disk or magnetic tape. There is a continuing strongly-felt need for increasing the data storage density in such media. Most efforts to increase magnetic data storage density involve techniques for increasing the areal bit density in the magnetic medium.
In rotating magnetic disk drives, the areal density is equivalent to the product of the number of flux reversals per millimeter and the number to tracks available per millimeter of disk radius. Thus, high areal data storage density requires recording heads with high linear resolution and narrow track-width. The linear resolution of a two-pole inductive head is related to the gap between the pole-tips at the air bearing surface (ABS). In the present art, submicron gaps are commonly available. Recent improvements in magnetoresistive (MR) sensor fabrication have led to development of the dual element head, which combines MR read and inductive write elements. This dual element approach solves the low read-back signal sensitivity problem associated with narrow inductive heads. Thus, increased linear recording density is now obtainable without incurring an unacceptable penalty in lost read signal sensitivity.
In pushing the areal density limit in magnetic recording using the dual MR-inductive element approach, the problems associated with fabricating narrow-track inductive write heads are now more limiting than the problems associated with fabricating narrow-track MR read heads. Experimental and mathematical modeling results confirm that further substantial increases in areal recording density must come from reductions in track width rather than from increases in linear flux transition densities in the recording media.
The major barrier to narrower track widths imposed by conventional thin film inductive head fabrication techniques is the topographical variation confronted when defining the upper pole-tip width. Because of varied topography, conventional thin film techniques require the narrow upper pole-tip to be deposited at the bottom of a 15-18 micron photoresist groove. Unreliable results are well-known for attempted deposition of a layer width of one to three microns at the bottom of a 15-20 micron groove depth. Several new pole-tip fabrication approaches have been proposed to address this problem.
Some practitioners avoid the track-width limitations of extreme topography by defining the upper pole-tip immediately following the deposition of the insulating material defining the recording gap. For instance, T. Kawabe, et al ("Fabrication of Thin Film Inductive Heads With Top Core Separated Structure", IEEE Transactions on Magnetics, Vol. 27, No. 6, November 1991, pp. 4936-4938) discusses a pole-tip stitching method where the pole-tip is formed earlier in the fabrication process where a thinner photoresist pattern can be used as a mask for the pole-tip.
Another approach is the overlapping or "staggered" pole-tip magnetic head design, which forms the narrow track width at the overlap of two wider pole-tips. Although the "staggered" head concept avoids the problems associated with fabricating pole-tips less than three microns wide, existing designs are subject to unacceptable side-writing effects at the "wrap-around" region 10 of the gap (FIG. 2). As used herein, a staggered pole head means any head design employing overlapping pole-tips to define a recording gap narrower than the pole-tips.
A ferrite head with overlapping poles that define the track width at the overlap (FIG. 1) was first suggested by D. L. Wallen in U.S. Pat. No. 2,961,495. Somewhat later, W. T. Frost, et al improved on this concept in U.S. Pat. No. 3,384,881. In both cases, the inventors showed how to make narrow track-widths without making small pole-tips. Neither practitioner suggests that a method for pole-tip alignment at the gap regions, however, and neither taught thin film applications.
A thin film version of the staggered pole-tip concept was first disclosed by Morimasa Nagao in U.S. Pat. No. 3,700,827. However, Nagao's design (FIG. 2) is not useful for modern applications because the upper pole P.sub.2 wraps around the lower pole P.sub.1, creating side-writing problems in wrap region 10 (FIG. 2).
Po-Kang Wang, et al ("Thin Film Head With Staggered Pole-tips", IEEE Transactions on Magnetics, Vol. 27, No. 6, November 1991, pp. 4710-4712) propose two staggered pole-tip configurations (FIGS. 3 and 4 ) for thin film inductive heads. The configuration in FIG. 3 is similar to a conventional thin film head except for the oversized pole-tips. The configuration in FIG. 4 differs significantly from the conventional head because the flux is conducted to the track region in a path that is parallel to the ABS. Wang, et al report that both configurations should be suitable for narrow track applications but they found that process variations reduced fabrication yields of staggered pole-tips in the transverse configuration and they were unable to obtain any significant yield of submicron track-widths in the longitudinal configuration. These problems were said to be related to the fabrication process.
FIG. 5 illustrates a typical planarization method known in the art for fabricating staggered pole-tips. FIG. 5A shows the deposition of the lower pole P.sub.1 element 12. FIG. 5B shows a nonmagnetic insulating layer 14 deposited over P.sub.1 layer 12. FIG. 5C shows the planarized lower pole assembly after removal of the excess material in FIG. 5B. In FIG. 5D, a gap-forming layer 16 is deposited on top of the planarized P.sub.1 layer 12. Finally, the upper pole P.sub.2 layer 18 is deposited to form the overlapping gap in FIG. 5D. While the Wang, et al designs (FIGS. 3 and 4) significantly improve the side-writing problem over Nagao's design (FIG. 2), more improvement is needed for submicron track applications. Further improvement can be obtained by using self-aligned pole-tips of the same width in the receding gap region at the ABS.
Until now, a staggered-pole inductive head with self-aligning pole-tips was unknown in the art. Because of the clearly-felt need for submicron track widths, the related unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.